Three types of spectral dominance recorded in AOT neurons of the honeybee, and their associated inhibitory pathways, as revealed by responses to chromatic combinations.

A) Broad-band (BB) ON-phasic neurons present similar excitatory responses to each spectral stimulus (upper curves). However, responses to chromatic mixtures reveal complete domination of longer wavelengths over shorter wavelengths (lower curves), suggesting inhibitory pathways (black arrows) that produce this suppressive phenomena. These neurons usually present smaller receptive fields (RFs) than BB ON-OFF or any color-opponent (CO) neuron type. B) CO UV+/B-/G- neurons respond with tonic excitation to UV and tonic inhibition to blue or green (upper curves). While a background of longer wavelength (e.g. green) inhibits (solid arrows) responses to any shorter wavelength (e.g. UV) added to the mixture (lower curves), a blue background also partially inhibits responses to green (dashed arrow). C) BB ON-OFF and CO UV(on)/B(on-off)/G(on-off) neurons while different in their responses to individual spectral stimuli (upper curves) presented very similar responses to chromatic mixtures (lower curves), with total inhibition of shorter wavelengths by longer wavelengths (solid arrows) and partial inhibition of longer wavelengths by a background of shorter wavelength. Therefore, ‘BB’ neurons as the ones illustrated in (A) and (C) are also connected to color-opponent circuits. Neuronal categories presenting OFF responses to single spectral stimuli and partial inhibition (dashed arrows) of shorter over longer wavelengths (B-C) have larger RFs than ON-phasic neurons (A).